基于线性光学系统实现量子密集编码

在线性光学系统中，提出了一个使用三光子GHZ态实现密集编码的方案。该方案中，Alice首先对她所持有的两个光子通过线性光学元件进行编码，然后将这两个光子传送给Bob. 接收到光子后Bob使用两个QND对等探测器以及PBS光学元件对他拥有的三个光子的八个量子态进行分辨，根据测量的结果辨别出Alice对她的两个光子所进行的操作。在密集编码过程中Alice仅传送两个光子，但Bob可以获得三比特的经典信息。探测使用的QND装置建立在cross-Kerr nonlinearity基础上，目前已经可以通过电磁感应透明实现。

Scheme for implementing quantum dense coding by using linear optical system

A novel scheme for realizing dense coding with Greenberger-Home-Zeilinger (GHZ)state in linear optical system is proposed. In this protocol, Alice codes on photon 1 and 2 by linear optical element and sents these photons to Bob. Then Bob performs a joint measurement on photons 1, 2, and 3 with the GHZ basis by employing two quantum nondemolition detectors (QND)and polarizing beam splitter (PBS). Eight GHZ states can be completely discriminated. According to the outcomes of his measurement, Bob can determine what operation Alice applied. Alice only transmits two photons in this process of the quantum dense coding, but Bob can obtain three bits of classical information. The QND devices are generally based on cross-Kerr nonlinearities, and the cross-Kerr nonlinearities are available with electromagnetically induced transparency (EIT).